When healthy Lee has been much more productive on a per game basis than R. McClain.
In 2013, in 11 games (and really less than 11 considering he missed a couple of halves), Lee had 99 tackles, 4 Interceptions, and 6 Passes defensed.
In 2014, in 6 games Rolando McClain has 31 tackles, 2 interceptions, and 2 passes defensed. He also has a sack.
Lee had the ability to run sideline to sideline and basically be involved in every tackle. Conversely, that ability is probably a bit of his downfall. He doesn't have the body type to be in on 'every' tackle and can't make it through a season.
My point with this post is not to say that I'd rather have Lee than Ro, it's just to point out then when healthy Lee is a MUCH more productive player.